Single-crystal study of the pressure-induced NaCl to CsCl type phase transition in KPF6 and the crystal structure of the high-pressure phase

The crystal structure of the high-pressure phase of bismuth gallium oxide, Bi2Ga4O9, was determined up to 30.5 (5) GPa from in situ single-crystal in-house and synchrotron X-ray diffraction. Structures were refined at ambient conditions and at pressures of 3.3 (2), 6.2 (3), 8.9 (1) and 14.9 (3) GPa for the low-pressure phase, and at 21.4 (5) and 30.5 (5) GPa for the high-pressure phase. The mode-Grüneisen parameters for the Raman modes of the low-pressure structure and the changes of the modes induced by the phase transition were obtained from Raman spectroscopic measurements. Complementary quantum-mechanical calculations based on density-functional theory were performed between 0 and 50 GPa. The phase transition is driven by a large spontaneous displacement of one O atom from a fully constrained position. The density-functional theory (DFT) model confirmed the persistence of the stereochemical activity of the lone electron pair up to at least 50 GPa in accordance with the crystal structure of the high-pressure phase. While the stereochemcial activity of the lone electron pair of Bi^{3+} is reduced at increasing pressure, a symmetrization of the bismuth coordination was not observed in this pressure range. This shows an unexpected stability of the localization of the lone electron pair and of its stereochemical activity at high pressure.

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Crystal structure of the high-pressure phase of calcium hydroxide, portlandite: In situ powder and single-crystal X-ray diffraction study

American Mineralogist ◽

10.2138/am.2013.4386 ◽

2013 ◽

Vol 98 (8-9) ◽

pp. 1421-1428 ◽

Cited By ~ 5

Author(s):

R. Iizuka ◽

T. Yagi ◽

K. Komatsu ◽

H. Gotou ◽

T. Tsuchiya ◽

...

Keyword(s):

Crystal Structure ◽

High Pressure ◽

Single Crystal ◽

Diffraction Study ◽

Calcium Hydroxide ◽

High Pressure Phase ◽

X Ray Diffraction ◽

X Ray ◽

Pressure Phase

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Crystal structure of a high-pressure phase of magnesium chloride hexahydrate determined by in-situ X-ray and neutron diffraction methods

Acta Crystallographica Section C Structural Chemistry ◽

10.1107/s2053229619014670 ◽

2019 ◽

Vol 75 (12) ◽

pp. 1605-1612 ◽

Cited By ~ 1

Author(s):

Keishiro Yamashita ◽

Kazuki Komatsu ◽

Takanori Hattori ◽

Shinichi Machida ◽

Hiroyuki Kagi

Keyword(s):

Crystal Structure ◽

High Pressure ◽

Neutron Diffraction ◽

Single Crystal ◽

Magnesium Chloride ◽

High Pressure Phase ◽

X Ray ◽

Magnesium Chloride Hexahydrate ◽

Chloride Hexahydrate ◽

Pressure Phase

A high-pressure phase of magnesium chloride hexahydrate (MgCl2·6H2O-II) and its deuterated counterpart (MgCl2·6D2O-II) have been identified for the first time by in-situ single-crystal X-ray and powder neutron diffraction. The crystal structure was analyzed by the Rietveld method for the neutron diffraction pattern based on the initial structure determined by single-crystal X-ray diffraction. This high-pressure phase has a similar framework to that in the known ambient-pressure phase, but exhibits some structural changes with symmetry reduction caused by a subtle modification in the hydrogen-bond network around the Mg(H2O)6 octahedra. These structural features reflect the strain in the high-pressure phases of MgCl2 hydrates.

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